di-TMP of the formula [C2H5C(CH2OH)2—CH2—]2-0, having the structure:
may also be referred to as 2-[2,2-bis(hydroxymethyl)butoxymethyl]-2-ethylpropane-1,3-diol. This material is of industrial significance as a valuable starting material for the production of alkyd resins, plasticizers and lubricants. di-TMP is found in high-boiling fractions and residues of the distillative work-up of the trimethylolpropane preparation. The prior art discloses processes for obtaining di-TMP from these residues.
According to DE 2058518 A1 (counterpart to U.S. Pat. No. 3,740,322 to Wada et al.), the di-TMP containing distillation residue is subjected to a steam distillation with superheated steam under reduced pressure. After removal of water, di-TMP is obtained from the resulting aqueous distillate, and can be recrystallized if required from an organic solvent, for example acetone.
DE 2358297 A1 (counterpart to U.S. Pat. No. 3,962,347 to Herz), discloses the simple crystallization of an aqueous solution of the distillation residue, wherein the salt concentration in the aqueous solution is adjusted to a particular ratio in order to enable the precipitation of di-TMP in sufficient purity.
US 2004/0254405 A1 discloses a process for recrystallization the distillation residue using organic solvents, for example acetone or methyl ethyl ketone, which requires a particular degree of observance for the crystallization temperature, the amount of solvent and the di-TMP content in the distillation residue. The use of a mixture of a suitable solvent and water for the isolation of di-TMP from the distillation residues of the trimethylolpropane preparation is described in DE 10 2008 038 021 A1 (counterpart to Publication 2012/0010435 of Rauchschwalbe et al.) An organic solvent phase and a viscous residue are initially obtained, the phases are separated and the organic solvent phase is extracted with water. The water phase is isolated and solvent residues present are removed. di-TMP is crystallized from the remaining water phase.
Various art relates to processes for obtaining di-TMP from secondary streams of the trimethylolpropane preparation. According to US 2013/0131391 A1 of Kreickmann et al., the high-boiling fractions and residues are dissolved in water and hydrogenated in the presence of an acidic compound to split formaldehyde-containing acetals. After removal of the solids, the hydrogenated material is then contacted both with basic and acidic ion exchangers. A trimethylolpropane-enriched product stream is distilled out of the aqueous eluate, and di-TMP remains as the distillation residue in sufficient quality.
Likewise WO2013/072008 A1 and WO2013/072006 A1 refer to the hydrogenation of the aqueous solution of the high-boiling fractions and residues in the presence of an acidic compound. After removal of the solid, low boilers are removed in a first distillation step. A trimethylolpropane-enriched product stream is obtained as a head fraction in a second distillation step and the bottom fraction is distilled in a third distillation step, in which di-TMP is obtained as the tops fraction and high boilers are removed as bottom fractions. According to WO 2013/072006 A1, a solid nickel catalyst is used in the hydrogenation step. Likewise, WO 2013/072007 A1 refers to a distillative process for obtaining di-TMP using a three- stage distillation process. In the first stage low boiling compounds and in the second stage intermediate boiling compounds are removed as tops fractions and the bottom fraction of the second distillation column is sent to a third distillation column in which di-TMP is obtained as a third distillation tops fraction and high boilers are removed as a bottom fraction.
Input stream for the distillation process according to WO 2013/072007 A1 is obtained, for e.g., in the preparation of trimethylolpropane as high-boiling fractions and residues with a certain content of di-TMP.
The art further refers to the deliberate or “on purpose” synthesis of di-trimethylolpropane from raw materials. According to EP 0 799 815 A1 (counterpart to U.S. Pat. No. 5,840,994 to Ninomiya et al.), trimethylolpropane is reacted directly with 2-ethylacrolein and formaldehyde in the presence of basic catalysts. After removing volatile components, purified ditrimethylopropane is obtained by recrystallization from water. According to WO92/05134 A1, already isolated trimethylolpropane is heated in the presence of an acidic compound, resulting in etherification to form di-trimethylolpropane.
JP2003335717 discloses the reaction of trimethylolpropane with the oxetane of trimethylolpropane (3-ethyl-3-hydroxymethyl-oxetane) in the presence of an acidic catalyst. So also, WO 01/14300 A1 discloses the ring opening reaction of trimethylolpropane oxetane with trimethylolpropane at elevated temperature in the presence of an acidic catalyst to provide ditrimethylolpropane. Neither reference provides guidance on an effective method to produce the oxetane of trimethylolpropane.
The oxetane of trimethylolpropane may be prepared by the reaction of trimethylol-propane with a carbamide, such as urea, in the presence of a catalyst such as zinc(II)acetate and potassium hydroxide according to U.S. Pat. No. 6,515,152 B1. See also GB 787,406 (Bayer). Other processes for preparing oxetanes per se using dialkyl carbonates or alkylene carbonates are discussed in Kokai Patent Application No. 10[1986]-7669 as well as Pattison, D. B., Cyclic Ethers Made by Pyrolysis of Carbonate Esters, J. Am. Chem. Soc., 1957, 79, vol 13, 3455-3456, Tan, Qiaohna et al. “Electrochemical Behaviors and Anion Recognition of Ferrocene Modified Hyperbranched Polyether.” Macromolecules. (Washington, D.C., USA), 42(13), 4500-4510; 2009.
WIPO Publication No WO 2014/024717 (PCT/JP2013/070485) discloses a process for making polyhydric alcohol ethers in which the alcohol is dehydrated and condensed.